Hydraulic circuit



Feb. 8, 1949. M. w. HUBER HYDRAULIC CIRCUIT Filed April l, 1946 k@H @H m E o @n I v S $3 hmm mm ww Nm Hm \m b m T mm l 2 71- E f, :Il L

. m md WH bmw l. om. .M302 mnrr patented Fein. 8, 194g f y' 1 Tnisinvendcn'relateswnydfe mission circuits, and p1'ovides ineens displacement i'tcr at dipprei:i1ii2i1ejly-'V onJ speed, by contioiliirg displacement ci avana abledisplacement pumpTw l i `The' invention was 'deyedjed use'iiia will be; described as iisedin tilt butwitl'it implying th'lt the nyenti l I to the p'diticnlir' `ld of uiie'.` All or e adyagntaes'cn b`e securediri other at'iplicaitin'I's of the inventivefcoicept. l f,

Gn' en aircraft, d pump wnienjfuijnisies hydreiulic liquid under pressure" for operdtirigsfc apparatus is `clistfiiemly'd'1iyje-rr d' by one of the propelling engines. quence it must run continuously W is in flight, eind at speeds"deterrny A y A speeds usueliy unrelated' to ine demanaffoi nydraiulic fluid.

T6 meer; these conditions @malienne ne ceT 's i f fe' enclin' is: :ineen-ated incidere-.iii ine com 'rfiemsfareconventional Y. L -ir ,,Illrelpnmpgtodyl'fleas p fitln which are elmp'edltliecyiiirdi asseiblyicmprisirig; nular cylinder block 3 and an annular guide bleek yp 19 geen@ Wil regirriiged;incirculan.sees;V trol is eiicie'nt, and imposes vvery li'ttlelc'dcn 30 r11-15e; Gf theseplimgeis expose inlet'poifts the ccntrclling mechanism'. The imprbyed 'p whenthep .eersereetrreclami;4 ,pori-sii is described and claimed n prior 'applicatiii l Serial No. 626,690, file'dNcvembeif 5, 1945; new' neet, Banfi flowing@ centrali chamber 9 fram Patent No. 2,433,222, issldl December; 23, 1941, Whilh, 1i1l`"i00'Its. -1 lead and in application Serial No. 757,621, filed Jiine' 27,1947. Y

Sometimes it is necessary to operate eidispl ment motor by hydraulic liquid delivered by engine driven pump and t limit the'speed @plunger ciose ehylrrdere. eteefvelves12 inici-'amitier yand thence yte' discharge by the motori The present invetionfeitt-ins tle 40 are: each @H result by putting the motor in circuit Witl el sp'onding spring l5 and, ,e ih13.&$z t-lilivlally Variable displacement 'punfp and subie tilting heed lf. 'lE-lfiehegdsl engage l @ffep displacement control mechanism of the pinp to af nich is @n his secondaryr (modifying) control- 'Which respcfii'ds 1- to motor speeds, as indicated by the i'fte at which y hydraulic liquid is discharged by the ymotor.

There are two possibilities. If the purpose is' merely to limit but not closely control the speed of the hydraulic motor,- a, reltiyely small cap"ateityV pump is used, i. e., one which at the maxim *In speed at which it is driven will furnjshrslifgntly more than the output required to drive the -nctor at the chosen limiting speed.

If the purpose is to meintainrnoter spe Pnf stent' over a'consid'erllerangeo p'uip speeds; l

hence receives o1 fromchamber`25 and supplies" it through radial ports 26 to the space in which the plunger-heads, swash plate and creep plate work. Hench, all parts run in oil.

Within chamber 25 each plunger B is encircled by a flanged, sleeve-like spill-back valve 21. Each such valve controls radial ports 28 in its plunger, and these radial ports lead from an axial port 29 bored from the end of the plunger. All the valves 21 are adjusted in unison by a plate 3i fixed on a stem 32 and engaging between ilanges on valves 21.

When stem 32 is in its left-most position, as shown in the drawing, ports 28 are closed by the initial displacing movements of plungers 6. If the y stem 32 is displaced to the right the spill-back ports are closed later in the displacing strokes of the plungers. They are not closed at all in the extreme right hand position of the Stem 32.

Stem 32 is guided in a bushing 33 pressed into a central aperture in vcylinder block 3, and the bushing 33 is formed at its right hand end with a small cylinder 34 in which a piston 35 works. Piston 35 is held on a reduced portion of stem 32 by a collar 36, and over a small annular area is subject to the head pressure developed by the pump. Pressure uid reaches the piston from chamber i3 through a combined strainer and choke 3'! and ports 38, 39.

As so far described the pump is essentially identical with that shown in Patent N o. 2,433,222.

Instead of a simple spring resisting the thrust of pressure uid to the right on piston 35, the stem 32 has a projecting end 4l which is slidable through a guide in cylinder head 42 of a cylinder 43, and engages a double acting piston 44 mounted in cylinder 43. The piston 44 is biased inward (to the left) by coil compression springs 45, 45. These, for convenience in mounting, are assembled with a center guide 41, two spring seats 48, 49 and a bolt 5| which holds the springs under partial compression when removed from the housing 52 in which they are enclosed. Spring seat 49 is adjustable to vary the spring loading by means of a screw 53 swiveledin cap 54 and threaded in a splined sleeve 55 which engages the spring seat.

As indicated in diagram, connection i4 is connected by line 56 with the supply connection of a displacement motor 51. By displacement motor is meant any motor whose speed is directly proportional to the volume of liquid passing through it. It could be an expansible chamber motor of either a rotary or reciprocating type, but if reciprocating, a multicylinder unit is advisable.

From the discharge connection of the motor a line 58 leads to a throttling unit 59 comprising a ported body having a ow throttling screw 6l locked in adjusted position by an acorn nut 62.

From the throttling unit 59 line 63 leads to sump 64, and from sump`54 suction line 65 leads to pump inlet connection 8.

The piston 44 is biased outward (to the right) by` a pressure diierential equal to the pressure drop through throttling unit 59. To effect this result the space to the left of piston 44 is connected by branch line 65 with line 58 close to fitting 59, and the space to the right of piston 44 is connected by branch line 61 with line B3 close to fitting 59.

Branch line 61 is not always strictly necessary. but is desirable as a safeguard against disturbing effects of back pressure in line 63, or changes of absolute pressure in sump 54. Such changes must be foreseen in airplane installations..

Operation Primary control is effected by head pressure acting Vto the right on piston 35 against the urge of springs V45, 46. If the motor tends to run too fast piston 44 is urged to the right by pressure developed in line 66 by the increased back pressure developed by tting 59. This is effective to reduce pump displacement and thus reduce the speed of the motor.

In one installation in which it was desired to limit motor speed to 240i) R. P. M. the primary adjustment of a pump proportioned as illustrated was set to maintain a discharge pressure of 1700 p. s. i. and the fitting 59 was adjusted for a pressure drop of only p. s. i. across the fitting.

It it is desired to hold the motor speed constant over a wide range of pump speeds, the pump should rate a considerable excess capacity when operating at top speed and full displacement. Even so, the pressure drop through tting 59 may still be small.

Excess pump capacity is not needed if the motor sped need be limited only near top pump speed.

As stated, the principle can be applied by the use of other variable capacity pumps, but the pump chosen for illustration has the advantages of sensitive control and high efficiency. Sensitive control permits the use of a low pressure drop at tting 59 and consequently saves energy.

In the accompanying drawing the pump is shown on a scale large enough to permit its construction to be understood. The diagrammatic representation of the motor is made without regard to scale.

In the claims the term movable abutment will be used as a generic term to include pistons, diaphragms and like equivalent components.

40 Since only the annular area at the periphery of piston 35 is effective, this piston has a very small eiective area on which the relatively high discharge pressure developed by the pump acts. Piston 44, however, is relatively large. It has many times the eiective area of piston 35, so

that it exerts a signicant, but secondary regulatory force when aiected by a small back pressure developed in tting 59.

What is claimed is:

l. A hydraulic unit comprising means for supplying liquid, a pump, a motor and connections such that the pump draws liquid from the liquid supplying means and discharges it through the motor; means for restricting the ow of liquid discharging from the motor; adjustable means for progressively varying the effective displacement of the pump; yielding means biasing said adjustable means in a direction to cause the pump to operate at full displacement; and two pressure responsive means arranged to react on said adjustable means in opposition to said bias the rst of which responds toiluid pressure in the connection between the pump and motor and the second of which responds to the back pressure developed by said flow restricting means.

2. A hydraulic unit comprising means for supplying liquid, a pump, a motor and connections such that the pump draws liquid from the liquid supplying means and discharges it through the motorf means for restricting the ow oi" liquid discharging from the motoryadjustable means for progressively varying the eiective displacement of the pump; yielding means biasing said adjustable means in a direction to cause the pump to operate at full displacement; and two pressure responsive means arranged to react on said adjustable means in opposition to said bias the first of which is a movable abutment of small effective area, subject to uid pressure in the connection between the pump and motor and the second of which is a much larger movable abutment subject to the back pressure developed by said flow restricting means. y

3. A hydraulic unit comprising means for supplying liquid, a pump, a motor and connections such that the pump draws liquid from the liquid supplying means and discharges it through the iotor; means for restricting the flow of liquid discharging from the motor; adjustable means for progressively varying the efective displacement of the pump; yielding moans biasing said adjustable means in a direction to cause the pump to operate at full displacement; and two pressure respcnsive means arranged to react on said adjustable means in opposition to said bias the 6 rst of which is a movable abutment of small effective area, subject to fluid pressure in the connection between the pump and motor, and the second of which is a rmuch larger double acting movable abutment subject in opposite directions to the pressures of liquid approaching and leaving said I'low restricting means.

MATTHEW W. HUBER.

I REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

